Relaxation oscillator



July 14, H R LUBCKE 2,047,277

RELAXATION OS C ILLATOR Filed May 23, 1954 Patented July 14, i936 r oFlcE I1 Claims.

In the following specication, and the accompanying drawing, I describe and show preferred means for accomplishing the objects of my invention. I do not limit myself to .5, the means disclosed however, and various changes and adaptations may be made without departing from the essence of the invention as hereinafter claimed.

My invention relates to the art of television,

10 and particularly to methods and means for the production'and synchronization of wave forms suitable for television scanning.

For electrical scanning by a television receiver of the cathode ray type, it is most desirable to be able to impress thereon sawtooth waveforms of electrical energy. Such waveforms may be applied to the means for defiecting the cathode rays, in well known ways; to cause the stream of electrons, and the light spot produced on the fluorescent screen thereby, to execute traverses across the receiving screen, synchronously with similar traverses across the field of View at the transmitter.

The prior art has been limited hitherto to sources of scanning energy which include several cooperating thermionic devices of the high vacuum type, when high quality results are desired; or to the use of single gaseous-discharge tubes, when inferior scanning waveforms can be tolerated. Y Y

` In my co-pending application No. 526,232, led March 30, 1931 I disclosed a source of scanning energy thatis capable of producing a high quality output; that is to say, a source having an out- 35 put of sawtooth wave-shape. In that output, the sloping sawtooth rises of the wave-shape are almost rectilinear; and the connecting portions are very steep, and consume relatively very small time intervals. But, to accomplish such results,

40 by the method of that disclosure, three separate thermionic tubes are required.

The Vlimitations of single gaseous discharge tubes; in which the deionization time of the gas limits the rapidity of the return portions of the 45 waveform between the peaks; and in which `the self-initiation of the time-constant circuit, in starting the successive waves, precludes a timeconstant value that gives good linearity;` are known to those skilled in the art. 50 An object of the present invention is to provide a single tube high vacuum thermionic source of scanning energy,- that'combines the advantages of multitube high vacuum devices with the simplicity of single tube devices. Y

Another object is to provide an oscillator of (Cl. Z50-36) the single tube multi-vibrator or relaxation type, in which the frequency of oscillation is independent of cathode emission.

A third object of the invention is to provide an oscillator having dynatron characteristics, 5 wherein the emission and wattage dissipation of usual thermionic devices is not exceeded.

My objects have been attained in the manner illustrated in the accompanying drawing, in Which- Fig. 1 is a diagrammatic representation of my improved source of energy for televisionl scanning;

Fig. 2 is a diagram illustrating the relation of the several electrode currents of my thermionic device to the inner grid voltage thereof; and

Fig. 3 shows the lvoltage waveforms that appear at the several electrodes of my thermionic device.

Referring to Fig. 1, reference numeral 5 indi- 20 cates the envelope of my single high-Vacuum thermionic device. This` includes; an electronemitting cathode K, that is heatable by a battery 6; three grids, G1, G2, and G3 respectively; and an anode or plate P. The last mentioned electrodes, in actual construction, preferably Vshould surround the cathode; grid G1 being closest to the cathode; grid G2 being at a greater distance therefrom, and therefore of larger diameter; grid G3 being still farther from the cathode, 30 and the largest in diameter; and plate P enclosing all of the other electrodes in the device.

One terminal of a resistor l, and one side of a condenser 3, are connected to each other and Vto grid G1, by a conductor 9. The other terminal of the resistor is connected to cathode K and to ground; and the other side of condenser 8 is connected to grid Gg by a conductor 23. This arrangement forms a time-constant circuit that largely determines the frequency of oscillations of the device. Grid G2 is connected atV Il to the highest positive voltage tap of a battery l2, orV other source of voltage, through a resistor I3. The latter usually may be of small Value, or even may be omitted under some conditions. Thus grid G2 serves largely as a means for accelerating electrons, in their ilight from the cathode. Grid G3 is connected to a considerably lower voltage tap of battery l2 at I4, through a resistor'l. This last mentioned grid thus has a 50 potential that is considerably'lower than that of grid G2, and it is adapted to emit secondary electrons. Consequently it is able to coact with grid G1, through condenser 8 to maintain relaxation oscillations. Plate P is connected, through V a resistor I6, to an intermediate voltage tap Il on battery I2. A condenser I8 is connected between plate P and cathode K, or directly in shunt to resistor I6; and, in cooperation with resistor I6, forms a second time-constant circuit that is adapted to modify the relaxation oscillations described supra. The energy wave-shape, resulting from this arrangement, has a sawtooth form with nearly rectilinear upward slopes, and rapid return traces connecting the peaks.

An alternating current generator, indicated at I9, schematically represents any source of short and sharp energy pulses, that are repeated at a frequency at or near the natural frequency of the relaxation oscillations of the described apparatus. Such pulses may occur in connection with a constant television scanning operation for example, and be in syntony with it. A conductor 2l, which should be considered as being diagrammatic of any communication means for transmitting such pulses, and therefore is shown dotted for a part of its length, establishes communication between generator I9 and grid Gs. synchronizing pulses also may be applied, if desired, to grids G1, or G2, or to plate P.

The lower part of resistor 'l is shown as being variable, to permit adjusting the natural frequency of the device to approximately the frequency of such incoming pulses as those described.

Energy from the above described scanning source may be delivered through conductor 22.

Relaxation oscillations are produced by the device described, because of the dynatron, or secondary emission, characteristic of grid G3. Such oscillations are responsible for the superior operation of the device as a source of scanning energy. The action may be explained as follows:

Assume, at rst, that cathode K is inoperative, and that it is not emitting electrons. Condenser 8 will then assume a charge, by reason of its connection to tap I4 on battery I2. At equilibrium, no current will flow, and therefore no voltage drop will occur in resistors 'I and I5. It will be seen that this puts the potential of grid G1 at zero, with respect to the cathode and ground.

Assume, next, that cathode K is put into operatio-n, and that it emits electrons. By referring to Fig. 2, which shows how the electrode currents of the device vary with respect to the potential of grid G1, it will be noted that when the potential of grid G1 is zero (i. e. at origin O), a large negative current will flow from grid G3. This is the result of the secondary electron emission of the grid. This negative current will raise the potential of grid G3 above that of tap Ill by reason of the potential drop in resistor I5. Consequently the upper plate of condenser 8 will become more positive also, since it is directly connected to grid G3 by conductor 23. The lower plate of condenser 8 naturally will simultaneously become more negative, in order to balance the charge on the upper plate. Therefore the potential of grid G1 becomes more negative also, since it is connected to the lower plate by conductor 9. As a result of this condition there will be an electronic surge from ground, through resistor l, condenser 8, grid G3, resistor I5, and battery I2. Electrons will flow from grid G3 to grid G2, since the latter is at a considerably higher potential, and therefore is able to attract a large part of the secondary emission from grid G3. With these two electronic paths in parallel, condenser 8 quickly becomes charged, and grid G1 assumes a relatively large negative potential. It will be seen from Fig. 2, that the above described actions will next cause the secondary emission current from grid G3 to reduce to zero; and the same thing is substantially true of all the other electrode currents.

The curves of Fig. 3 show how the potentials on the several electrodes vary throughout the operating cycle of the device; slightly more than o-ne complete cycle of each potential waveform being shown, substantially as it would appear on an oscillogram. At the above stated point in the operating cycle when the thermionic device becomes inactive, the charge on condenser 8 leaks off to ground through resistor l; and the potential of grid G1 thus becomes less negative. and approaches zero with respect to the cathode. This action is governed by the exponential discharge curve of the condenser, and corresponds with curve e-G1 of Fig. 3 between the points 25 and 2G.

Referring again to Fig. 2, and remembering that the cathode is now being considered as emitting, we see that, as grid G1 approaches zero potential, an electronic current starts to flow from cathode K to this grid. This is indicated by curve I-G1. This current, flowing through resistor l, causes grid G1 to become negative, and halts the positive swing thereof. Furthermore, grid G3 is now emitting secondary electrons, and is further causing grid G1 to become negative. These combined agencies make grid G1 quickly swing to a large negative value.

It will be noted that the operating cycle of grid G1 carries it from a large negative potential, of a value determined by the efficacy of the agencies operating to charge condenser 8, and under which conditions the thermionic device is inoperative; to a value slightly beyond zero potential, where the current from grid G1, and the secondary emission from grid Gs, reverse the cycle. Thus (referring to Fig. 2) the value of the potential on grid G1 moves along the horizontal axis (abscissae) from the left, to a point to the right of the vertical axis (ordinates). It does this at a comparatively slow rate during the discharge of condenser 8, and at a rapid rate during the charge thereof. The actual variation of potential on grid G1 is shown by curve e-G1 of Fig. 3.

It will be apparent from the foregoing, that my thermionic device does not continuously work at large saturation currents, in the manner that is characteristic of single tube multivibrators or relaxation oscillating devices. In a test of a typical device of my improved form, the average currents drawn from cathode K, as measured with direct current instruments, were IG2=}.8 m. a.; IG3=-.l.1 m. a.; and Ip=+-75 In. a.; giving a total of 1.44 m. a., with a useful output of 20 volts, peak to peak, of alternating current waveform, the frequency being 1,200 cycles. The normal rating of the thermionic device, used as an amplifier, was 2.5 m. a., and the cathode was of a size and rating allowing a current of 5 m. a. when coacting with a triode arrangement of elements. Typical values for the taps on battery I2, were; for tap II, 170 volts; for tap I4, 67 volts; and for tap Il, volts.

By suitably varying the lcapacitance of condenser 8, or the resistance of resistor 'I, outputs of from 2 to 75 volts peak to peak may be obtained at frequencies from 6000 to cycles per second. Of course, any frequency and output can be achieved, by a proper choice of values for the respective elements.

In the prior art, the dependence of operating frequency upon cathode emission, and the practical impossibility of maintaining a desired irequency stability, because of this edect, are well known. In my now disclosed devic-e, repeated tests have shown that the frequency of operation is constant within about 2%; while the cathode supply voltage is decreased from its rated value, to 64% of its rated value. At the latter point the device ceases to operate.

While my invention resembles certain prior devices in some ways, it is essentiaily different therefrom in the respects mentioned, and in certain other respects. These essential differences enable it to function Yin a superior manner that has not been attainable by ways that have been known hitherto. Thus, Fig. 2 indicates that plate current I-P is almost independent oi the voltage of grid G1. rlhe plate, being thus uncontrolled by the inner grid, is tree to respond to the impulses oi outer grid G3, (see curve e-G of Fig. 3) and its output is a sawtooth wave like that shown at ee-l? in Fig. 3. rlhis fact, and the further fact that the time-constant value of elements I5 and i8 exercise a denite, although secondary eiiect, upon the the frequency of operation of my device, shows that it enters into the relaxation oscillation process; and that it functions in a manner that could not be attained by additions to devices of the prior art. rihe diiference in operation over prior art devices is further evidenced by the fact that the direct current potential of the anode also aiects the frequency of my device.

The voltage waves shown in Fig. 3 bear a striking resemblance to corresponding oscillograms taken from a three tube scanning source like that described in my pending patent application referred to supra. Thus, with reference to said pending application, the present curve e-Gri is very similar in shape and phase to the grid po tential curve of the rst multivibrator tube disclosed in that application. Correspondingiy, curve e-Gz is similar to the plate potential curve of the rst multivibrator tube, and to that of the grid of the second multivibrator tube; curve e-G3 is similar to the plate potential curve of the second multivibrator tube; and curve om? is similar to the plate potential curve of the third, or peaking tube, Y

The same time scale is used in all of the curves of Fig. 3. Thus, corresponding points in cmves vertically above each other occur at the same time in the operatingcycle. heavy lines ci the waveforms of Fig. 3 indicate a comparatively slow change of potential with time, as in ea-Gi from point 25 to point 2li; whereas the light lines indicate a rapid change, as from point 2l to point 28. This is as the waveforms appear in cathode ray oscillograms.

From the foregoing disclosure, it will appear that the present invention comprises a new combination of elements that are so arranged and connected as to adapt them to secure, in a single thermionic device, results that could only be attained hitherto by the use of several tubes. Moreover, my present device functions in an entirely new way, in that it makes effective use of secondary emission from grid G2. It is a relaxation dynatron oscillator that employs resistive and capacitative elements only. It is notable that curve I-G3 shows that the entire operating range of the current value in grid Gs may be wholly the result Yof a secondary emission current (the net electron flow always being from the electrode, rather than to it).

In the foregoing description, I necessarily have disclosed specic means whereby the stated objects of my invention may be attained; but the invention is not to be considered as limited to the use of such specific means, except as expressed in the appended claims.

l-laving thus fully described my invention, I

claiml. An energy source which includes a thermionic device having a cathode, an anode, and three grids; the cathode and the grid nearest thereto being connected to each other; the next grid in order being connected to a source of positive voltage; the third grid in order being connected to the first said grid through a condenser, and also to a source of positive voltage of vless value than that first mentioned; and the anode being connected to the cathode through a condenser, and also to a source of positive voltage that is intermediate in value with respect to the first and second sources mentioned.

2. An electrical energy source which includes a thermionic device having a cathode, an anode, and three grids; the cathode being connected to ground; the grid nearest the cathode being connected to ground through a resistor; the next grid in order being connected to a source of positive voltage; the third grid in order being'connected to the first said grid through a condenser, and also being connected through a resistor to a source oi positive voltage of less value than that iirst mentioned; and the anode being connected to ground through a condenser, and also being connected through a resistor to a source of positive Voltage that is intermediate in value with respect to the rst and second sources.

3. A source o oscillating energy which includes a thermionic device having a cathode, an anode, and three grids differently spaced between the cathode and the anode; the cathode being connected to ground; the grid nearest the cathode being connected to ground through a resistor; the intermediate grid being connected to a source of positive voltage; the grid nearest the anode being connected to the first said grid through a condenser, and also being connected through a resistor to a source of positive voltof less value than that rst mentioned; and the anode being connected to ground through a condenser, and also being connected through a resistor to a vsource o1 positive voltage that is intermediate in value with respect to the rst and second voitage sources mentioned; the last said grid being adapted to emit secondary electrons, and to thereby cause said device to operate as an oscillator.

d. An oscillator comprising; a thermionic device having'a cathode, an anode, and three intermediate grids; and a source of direct current energy of which the negative terminal is connected to the cathode; the cathode and the grid nearest thereto being connected to each other through resistor; the second grid in order being connected to a positive terminal of said source; the third grid being connected to the rst grid through a condenser, and also through a resistor to a positive terminal of said source at a potential level below that ofthe connection to the second grid; and the anode being connected to the cathode through a second condenser, and also to a positive terminal of said source; the constants of the oscillator being of such value that the third grid is adapted to emit a secondary electronic current of greater value than it can receive from the cathode, throughout the operating cycle of the oscillator.

5. An oscillator comprising; a high vacuum thermionic device having a cathode, an anode, and three intermediate grids; and a source of direct current energy of Which the negative terminal is connected to the cathode; the cathode and the grid nearest thereto being connected to each other through a resistor; the second grid in order being connected to a positive terminal of said source; the third grid being connected to the rst said grid through a condenser, and also being connected through a resistor to a positive terminal of said source at a potential level below that of the connection to the second grid; the anode being connected to the cathode through a condenser, and also to a positive terminal of said source at a potential level intermediate connections to the second and third grids; the constants of the oscillator being of such value that the third grid is adapted to emit a secondary electronic current, and to produce sawtocth pulses of electrical energy in said condenser.

An oscillator as defined in claim 5, wherein the constants of the oscillator are so chosen that the anode current is made independent of the potential of the first said grid by virtue of said secondary emission.

'7. An oscillator comprising; a thermionic device having a cathode, an anode, and three intermediate grids; and a source or" direct current energy of which the negative terminal is connected to the cathode; the cathode and the grid nearest thereto being connected to each other through a resistor; the second grid in order being connected to a positive terminal of said source; the third grid being connected to the first grid through a condenser, and also through a resistor to positive terminal of said source; and the anode being connected to the cathode through a second condenser, and also to a positive terminal or" said source; the operating periodicity of the oscillator being controllable by varying the position of the last said terminal with respect to its potential level, to regulate the electronic current nov/ing in. said device and thus to limit the charging currents to the respective condensers.

8. A relaxation oscillator comprising; a high vacuum thermionic device having a cathode, an anode, and three intermediate grids; and a source of direct current energy of which the negative terminal is connected to the cathode; the cathode and the grid nearest thereto being connected to each other through a resistor; the second grid in order being connected to a positive terminal of said source; the third grid being connected to the rst grid through a condenser, and also through a resistor to a positive terminal of said source at a potential level below that of the connection to the second grid; and the anode being connected to the cathode through a second condenser, and also, through a resistor, to a positive terminal of said source; the periodicity of the relaxation pulses of the oscillator being controllable by varying the time constant of the anode circuit.

9. A relaxation oscillator comprising; a single high vacuum thermionic device having a cathode, an anode, and three intermediate grids; and a source o direct current energy of which the negative terminal is connected to the cathode; the cathode and the grid nearest thereto being connected to each other through a resistor; the second grid in order being connected to a positive terminal of said source; the third grid being adapted to emit secondary electrons, and being connected through a resistor to a positive terminal of said source at a potential level belovv that of the connection to the second grid; the anode being connected to the cathode through a condenser, and also to a positive terminal of said source; and means for impressing electric pulses upon the third grid to change its potential, and thereby to vary the secondary emission therefrom to control the periodicity or the oscillator.

l0. An oscillator comprising; a thermionic device having a cathode, an anode, and three intermediate grids; and a source of direct current energy of which the negative terminal is connected to the cathode; the cathode and the grid nearest thereto being connected to each other through a resistor; the second grid in order being connected to a positive terminal of said source; the third grid being connected to the rst grid through a condenser, and also, through a second resistor, to a positive terminal of said source at a potential level below that of the connection to the second grid; and the anode being connected to the cathode through a second condenser, and also to a positive terminal of said source at a potential level intermediate the connections to the second and third grids; the third grid being adapted to emit secondary electrons when the rst condenser has become partially discharged, thus permitting that condenser to become re-charged.

1l. A relaxation oscillator comprising; a high vacuum thermionic device having a cathode, an anode, and three grids that are differently spaced in relation to the cathode and anode; and. a source of direct current energy of which the negative terminal is connected to the cathode; the cathode and the grid nearest thereto being connected to each other through a resistor; the second grid in order being connected to a positive terminal of said source; the third grid being connected to the first grid through a condenser, and also to a positive terminal of said source; and the anode being connected to the cathode through a second condenser, and also to a positive terminal of said source at a potential level intermediate the connections to the second third grids; the periodicity of the relaxation pulses of the oscillator being controllable by varying the value of the time constant of the resistor and rst condenser combination.

HARRY R. LUBCKE. 

